1. Field of the Invention
The present invention relates to a method of manufacturing a light emitting diode, and more particularly, to a method of manufacturing a light emitting diode with a current blocking structure.
2. Description of the Prior Art
Please refer to FIG. 1. FIG. 1 is a schematic diagram of a light emitting diode 10 according to the prior art. The dashed lines shown in FIG. 1 indicate the current flow. The AlGalnP quaternary compound semiconductor material is a promising material for making a light emitting diode with emission wavelength ranging from 650 nm to 560 nm. However, the AlGalnP material with high aluminum content is very difficult to dope heavily in P-type. Normally, a light emitting diode 10 using N-type GaAs 12 as substrate has a P-type AlGaInP upper cladding layer 14 near the upper electrode 16 as shown in FIG. 1. Due to low mobility and low carrier concentration, the P-type AlGalnP upper cladding layer 14 has higher resistivity. Therefore, the injected current would be restricted to flow only through the active layer 18 that is underneath the upper electrode 16. Because the light generated only from the active layer 18 which is underneath the upper electrode 16, most of the light would be absorbed by the opaque upper electrode 16 as shown in FIG. 1. The luminous intensity of the light emitting diode 10 is not very high. In order to solve the current crowding problem, a large bandgap and low resIstivity thick window layer was proposed by U.S. Pat. No. 5,008,718 to enable current to spread out the contact and reduce contact shadowing. Because it is difficult to find out large bandgap and at the same time lower resistivity semiconductor material, thick window layer is required to ensure effectively spreading the current to the edge of the LED chip.
Please refer to FIG. 2. FIG. 2 is a schematic diagram of a light emitting diode 20 with a current blocking structure 22. The dashed lines shown in FIG. 2 indicate the current flow. U.S. Pat. No. 5,048,035 proposed a current blocking structure 22 which can very effectively shift the drive current out the patterned portion of the upper electrode 24. But the current blocking structure 22 shown in FIG. 2 needs two steps epitaxial growth. Therefore, it is very difficult to grow the whole LED structure with high yield.
Please refer to FIG. 3. FIG. 3 is a schematic diagram of a light emitting diode 30 with a patterned metal contact 32. U.S. Pat. No. 4,884,370 proposed a light emitting diode 30 which has a dielectric layer 34 beneath a patterned metal contact 32 as shown in FIG. 3. The patterned metal contact 32 is insulated from the structure of the light emitting diode 30 to prevent current flow and subsequent light generation underneath the patterned metal contact 32. However, the dielectric layer 34 is placed directly below the patterned metal contact 32 and far away from an active layer (not shown) of the light emitting diode 30. Part of the current pushed away from the patterned metal contact 32 would be pulled back under the patterned metal contact 32. Therefore, it is not very effective to solve the current crowding problem. Besides, the contact region between the ohmic contact metal and the upper semiconductor layer is smaller than the ordinary light emitting diode 30. The contact resistance may increase due to the reduction of the contact area. If the adhesion between the dielectric layer 34 and the patterned metal contact 32 or between the dielectric layer 34 and the upper semiconductor layer is not good, it would also cause the peeling off problem of the patterned metal contact 32.
It is therefore a primary objective of the present invention to provide a method of manufacturing a light emitting diode with a current blocking structure to solve the above mentioned problem.
In the preferred embodiment, the present invention provides a method of manufacturing a light emitting diode based on an epitaxial layer structure. The epitaxial layer structure comprises a substrate of a first conductivity type, a lower cladding layer of the first conductivity type formed on a top side of the substrate, an active layer formed on the lower cladding layer, an upper cladding layer of a second conductivity type formed on the active layer, at least one upper aluminum-rich layer formed on the upper cladding layer, and a cap layer formed on the at least one upper aluminum-rich layer. The method comprises:
forming an opening hole in the epitaxial layer structure for passing through each upper aluminum-rich layer;
oxidizing a predetermined region of each upper aluminum-rich layer;
filling the opening hole with an insulating material; and
forming an upper electrode on the cap layer and a lower electrode on a back side of the substrate.
It is an advantage of the present invention that the predetermined region can act as a current blocking structure so that the current can spread out of the predetermined region. Therefore, the light generated from the active layer will not be blocked by the upper electrode. The luminous intensity of the light emitting diode can be increased at least 50% compared to the light emitting diode without the current blocking structure.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment which is illustrated in the various figures and drawings.